It is demanded of the reflecting electrode film of a color liquid crystal display to have heat resistance enough to stand against heating because it is heated to about 250° C. in the heating step for assembling a color filter in the production of a color liquid crystal display and the like. Al and alloys containing Al as a major component have been used as the reflecting electrode film, and silver alloys are being examined as the reflecting electrode film material with expectation of a high reflectance and low electric resistance.
The applicant of the invention has disclosed a Ag (silver)-Pd (palladium)-Cu (copper) type silver alloy as the silver alloy suitable to a reflecting electrode film and a reflecting wiring electrode film (see Patent References 1 to 3).
Patent Reference 1: Japanese Patent Application Laid-Open (JP-A) No. 2000-109943, Claim 4.
Patent Reference 2: JP-A No. 2001-192752, Claim 1.
Patent Reference 3: f JP-A No. 2001-226765, Claim 2.
The Ag—Pd—Cu type silver alloys described in the above Patent references 1 to 3 are more improved in weatherability than pure silver. A reflecting electrode film made of a Ag—Pd—Cu type silver alloy gave rise to the growth of surface roughness and generation of hillocks though these phenomena occurred not a few, causing dropped reflectance as described later. Also, sulfurization is promoted by heating and the resistance of the alloy to the sulfurization has been improved only insufficiently. Along with the sulfurization of the Ag—Pd—Cu type silver alloy, yellowing of the reflecting electrode film has been caused, bringing about a reduction in the luminance of a color liquid crystal display. This is the reason why there has been a great need to find a silver alloy having a higher performance, specifically, higher heat resistance and high resistance to sulfurization that have not been obtained so far.
In the meantime, an invention is disclosed in which Ge (germanium) is compounded in a Ag—Pd type silver alloy for a reflecting film of an optical recording medium such as CD-ROMs that are not processed in a heating step when a color liquid crystal display is produced (see, for example, Patent Reference 4). Here, Ge is assumed in the invention to have an effect of improving the weatherability of a silver alloy, specifically, the effect of preventing the lowering of reflectance caused by long-term use of the reflecting film.
Patent Reference 4: JP-A No. 2003-193155, Claim 1.